There is an increasing concern over the disposition of plastic waste. Many jurisdictions are seriously considering recycle content regulations requiring a specified percentage of plastic to be recycled. While this is seen as a politically and socially acceptable goal there are some concerns with some recycled plastics.
More particularly there is a concern with plastics which have been used in the food or medical fields. In the area of rigid plastic used in the packaging, display, and consumption of raw and cooked foods there is a concern with protein containing contaminants such as meat, blood and often the condiments used in association with cooked foods. Meat and blood residues are of particular concern as such contaminants tend to be difficult to remove. Of course this causes difficulties with sorting and preparation for recycling rigid plastic waste. The above concerns are even further heightened when medical wastes are considered.
In conventional cleaning methods the plastic recycle is cleaned either prior to or after shredding. The conventional methods require the use of hot water and cleaning agents such as detergents, surfactants, soaps and the like. Additionally, even if the washing medium, typically water is recycled, it must then be reheated. This is energy consuming.
WPI Accession no. 91-264337/36 of Japanese Patent 3175008 discloses a process in which agricultural film is pretreated to remove most of the dirt (e.g. the big lumps), ultrasonically washed, dewatered, crushed (fluffed) sorted and collected. The patent does not disclose the treatment of rigid polymers from the food or medical industries. Additionally, the reference requires a pre-washing step which has been eliminated from the process in accordance with the present invention.
WPI Accession no. 84-304130/49 of Japanese patent 59189946 discloses a process for treating waste plastic films. In the process the film is rough washed, dewatered, subjected to a water cutter (i.e. lance or knife or the like) which cuts and rewashes the film pieces, dewatered and finally washed with warm water in an ultrasonic wash tank. The reference deals with film and contains a number of pretreatment steps which are avoided in a process in accordance with the present invention. Additionally, the present invention contemplates the use of a washing medium at substantially ambient temperatures and in a preferred embodiment the multiple use or recycling of the washing medium.
Accordingly, there is a need for a simple economic process to clean waste rigid plastic used in the food or medical industries.